As I understand is the AGM has nothing to do with the chemistry of the battery, but dictates that it's suitable for auto start/stop engine applications. Maybe I'm wrong.
Regardless the yuasa HSB053 is listed in Halfords AGM battery lineup. Not that I trust them but I felt I could take it as sufficient.
Most important for batteries within the cabin is that they are properly vented. Which also the HSB053 comes with dual vent. Just be sure to add a plug to the unused vent.
Edit: your right! AGM is not then the star stop suitability of the battery. Seems I want to look at an alternative. Humm. Tried to update my post above, but can't. Regardless I'll not by tying myself down to the one battery on the market that has that oversized vent. Will swap for any AGM that fits the other specs.